U.S. patent number 10,873,243 [Application Number 15/795,492] was granted by the patent office on 2020-12-22 for electrical machine.
This patent grant is currently assigned to ROLLS-ROYCE PLC. The grantee listed for this patent is ROLLS-ROYCE plc. Invention is credited to Ellis F H Chong, Geraint W. Jewell, Adam J. McLoughlin.
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United States Patent |
10,873,243 |
Jewell , et al. |
December 22, 2020 |
Electrical machine
Abstract
An electrical machine comprising a two-part rotor formed of a
first rotor part and a second rotor part. The first rotor part
includes a conical section and is mounted to a shaft of the
machine. The second rotor part has a bore including a complementary
conical section. The second rotor part is configured to displace
axially between a first state, in which it is engaged with the
first rotor part to form the rotor of the electrical machine, and a
second state, in which it is axially disengaged from the first
rotor part. Also a clutch having an engaged state and a disengaged
state. When the clutch is in one of its states the second rotor
part is in its first state and switching the clutch to the other of
its states axially displaces the second rotor part to its second
state.
Inventors: |
Jewell; Geraint W. (Sheffield,
GB), McLoughlin; Adam J. (Derby, GB),
Chong; Ellis F H (Derby, GB) |
Applicant: |
Name |
City |
State |
Country |
Type |
ROLLS-ROYCE plc |
London |
N/A |
GB |
|
|
Assignee: |
ROLLS-ROYCE PLC (London,
GB)
|
Family
ID: |
1000005258639 |
Appl.
No.: |
15/795,492 |
Filed: |
October 27, 2017 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20180131250 A1 |
May 10, 2018 |
|
Foreign Application Priority Data
|
|
|
|
|
Nov 4, 2016 [GB] |
|
|
1618616.5 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F16D
11/14 (20130101); F16D 27/01 (20130101); H02K
7/1823 (20130101); F16D 27/108 (20130101); H02K
7/1085 (20130101); H02K 7/125 (20130101); H02K
1/272 (20130101); F16D 27/118 (20130101); F05D
2260/403 (20130101); F02C 7/36 (20130101); Y02E
10/72 (20130101) |
Current International
Class: |
H02K
7/108 (20060101); H02K 1/27 (20060101); H02K
7/12 (20060101); H02K 7/18 (20060101); F16D
11/14 (20060101); F16D 27/01 (20060101); F16D
27/108 (20060101); F16D 27/118 (20060101); F02C
7/36 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
101577463 |
|
Nov 2009 |
|
CN |
|
104836372 |
|
Aug 2015 |
|
CN |
|
571367 |
|
Mar 1933 |
|
DE |
|
852573 |
|
Oct 1952 |
|
DE |
|
1062340 |
|
Nov 1954 |
|
DE |
|
2728140 |
|
May 2014 |
|
EP |
|
2242575 |
|
Oct 1991 |
|
GB |
|
Other References
Great Britain Search Report dated May 15, 2017, issued in GB Patent
Application No. 1618616.5. cited by applicant .
European Search Report dated Mar. 23, 2018, issued in EP Patent
Application No. 17194982. cited by applicant.
|
Primary Examiner: Nguyen; Tran N
Assistant Examiner: Pham; Leda T
Attorney, Agent or Firm: Brinks Gilson & Lione
Claims
The invention claimed is:
1. An electrical machine comprising: a two-part rotor having a
rotational axis and formed of: a first rotor part which includes a
conical section and which is mounted to a shaft of the machine; a
second rotor part positioned radially outside the first rotor part
and which has a bore including a complementary conical section, the
second rotor part configured to displace axially between a first
state, in which the second rotor part is engaged with the first
rotor part to form the rotor of the electrical machine, and a
second state, in which the second rotor part is axially disengaged
from the first rotor part, the second rotor part including an
annular array of permanent magnets on an outer periphery; a stator
including electrical coils and being positioned radially outside
the two-part rotor; and a clutch having an engaged state and a
disengaged state; wherein when the clutch is in one of the engaged
and disengaged states the second rotor part is in the first state,
wherein a switch of the clutch to the other of the engaged and
disengaged states axially displaces the second rotor part to the
second state, and wherein the clutch comprises an electromagnetic
actuator.
2. An electrical machine as claimed in claim 1 wherein when the
clutch is in the engaged state the second rotor part is in the
first state and a switch of the clutch to the disengaged state
axially displaces the second rotor part to the second state.
3. An electrical machine as claimed in claim 1 wherein when the
clutch is in the disengaged state the second rotor part is in the
first state and a switch of the clutch to the engaged state axially
displaces the second rotor part to the second state.
4. An electrical machine as claimed in claim 1 wherein the
electromagnetic actuator includes a DC coil.
5. An electrical machine as claimed in claim 4 wherein the
electromagnetic actuator further comprises one or more permanent
magnets.
6. An electrical machine as claimed in claim 1 wherein the clutch
comprises a non-rotating member and a rotating member, the rotating
member coupled to the second rotor part.
7. An electrical machine as claimed in claim 6 wherein the
non-rotating member comprises a coil and the rotating member
comprises a ferromagnetic plate.
8. An electrical machine as claimed in claim 1 wherein the
electrical machine comprises a permanent magnet electrical
machine.
9. An electrical machine as claimed in claim 1 wherein the conical
section and the complementary conical section include positive
engagement features.
10. An electrical machine as claimed in claim 9 wherein the
positive engagement features comprise splines.
11. An electrical machine as claimed in claim 1 wherein the first
and second rotor parts each comprise more than one complementary
conical section.
12. An electrical machine as claimed in claim 1 further comprising
a bias member to bias the second rotor part into the second
state.
13. An electrical machine as claimed in claim 12 wherein the bias
member is selected from the group consisting of a compliant member,
a spring, and a Belleville washer.
14. An electrical machine as claimed in claim 1 further comprising
a bias member to bias the second rotor part into the first
state.
15. An electrical machine as claimed in claim 1, wherein the
electrical machine is a generator and the electromagnetic actuator
is configured to position the second rotor part in the second
state, in which the second rotor part is axially disengaged from
the first rotor part.
Description
CROSS-REFERENCE TO RELATED APPLICATION
This application is based upon and claims the benefit of priority
from British Patent Application Number 1618616.5 filed 4 Nov. 2016,
the entire contents of which are incorporated by reference.
BACKGROUND
The present disclosure concerns an electrical machine with a
mechanical disconnect. In particular it concerns a permanent magnet
electrical machine with a mechanical disconnect.
BRIEF SUMMARY
According to a first aspect there is provided an electrical machine
comprising: a two-part rotor having a rotational axis and formed
of: a first rotor part which includes a conical section and which
is mounted to a shaft of the machine; a second rotor part which has
a bore including a complementary conical section, the second rotor
part configured to displace axially between a first state, in which
it is engaged with the first rotor part to form the rotor of the
electrical machine, and a second state, in which it is axially
disengaged from the first rotor part; and a clutch having an
engaged state and a disengaged state; wherein when the clutch is in
one of the engaged and disengaged states the second rotor part is
in its first state and wherein switching the clutch to the other of
its engaged and disengaged states axially displaces the second
rotor part to its second state.
Advantageously the two-part rotor enables the electrical machine to
be stopped without stopping the first rotor part from rotating.
Advantageously the electrical machine is therefore suitable to be
mounted to a shaft of a gas turbine engine or other shaft which
cannot be stopped in normal operation. Advantageously the
electrical machine can be stopped in the event of a fault or when
it is not required because its operation is not tied to the
operational period of the prime mover of the shaft.
When the clutch is in its engaged state the second rotor part may
be in its first state. Switching the clutch to its disengaged state
may axially displace the second rotor part to its second state.
Advantageously the clutch is only energised when it is desired to
engage the rotor of the electrical machine. Advantageously the
rotor parts will disengage in the absence of clutch engagement so
the arrangement will fail safely if the clutch cannot be
energised.
Alternatively when the clutch is in its disengaged state the second
rotor part may be in its first state. Switching the clutch to its
engaged state may axially displace the second rotor part to its
second state. Advantageously the clutch only needs to be energised
to disengage the rotor parts and therefore stop the electrical
machine. Advantageously in normal operation when it is desirable to
have both the machine shaft and the electrical machine operating
the clutch does not require energy.
The clutch may comprise an electromagnetic actuator. The
electromagnetic actuator may include a DC coil. The electromagnetic
actuator may further comprise one or more permanent magnets.
Advantageously the clutch may be engaged by applying a current
through the DC coil. Advantageously the current required may be
small.
The clutch may comprise a non-rotating member and a rotating
member. The rotating member may be coupled to the second rotor
part. The rotating member may be a part of the second rotor part,
for example an axial end of the second rotor part or a protrusion
therefrom. The non-rotating member may comprise a coil. The coil
may be a DC coil. The rotating member may comprise a ferromagnetic
plate. The electrical machine may comprise a permanent magnet
electrical machine.
The complementary conical sections may include positive engagement
features. The positive engagement features may comprise splines.
Advantageously positive engagement features may improve the
engagement between the conical sections of the first and second
rotor parts of the electrical machine. Alternatively the
complementary conical sections may engage through frictional
contact. The complementary conical sections may include surface
features to increase the friction therebetween, for example surface
roughening.
The first rotor part may comprise more than one conical section.
The second rotor part may comprise more than one conical section.
Advantageously a first rotor part with more than one conical
section may be suitable to engage with and complement different
second rotor parts having a single conical section. Advantageously
this reduces manufacturing costs for producing different machines.
Similarly a second rotor part with more than one conical section
may be suitable to engage with and complement different first rotor
parts having a single conical section. Advantageously this reduces
manufacturing costs for producing different machines.
The first and second rotor parts may each comprise more than one
complementary conical section. For example the first rotor part may
have two conical sections and the second rotor part may have two
complementary conical sections. The two conical sections on each
rotor part may be contiguous or spaced apart by a non-conical
section. There may be more than two complementary conical sections,
any adjacent two of which may be contiguous or spaced apart. The
first rotor part may have a different number of conical sections to
the second rotor part. The first rotor part may have more conical
sections than the second rotor part or the first rotor part may
have fewer conical sections than the second rotor part.
The electrical machine may further comprise a bias member to bias
the second rotor part into its second state. Advantageously the
bias member provides a restoring or returning force which opposes
the force from the clutch. Advantageously the bias member more
reliably separates the second rotor part from the first rotor part
and therefore disengages the electrical machine. Alternatively the
electrical machine may further comprise a bias member to bias the
second rotor part into its first state. Advantageously the bias
member provides a restoring or returning force which opposes the
force from the clutch. Advantageously the bias member helps to
ensure that the rotor parts engage fully. The bias member may
comprise one of a compliant member, a spring, a Belleville washer.
The bias member may comprise more than one compliant member,
multiple springs or multiple Belleville washers.
The skilled person will appreciate that except where mutually
exclusive, a feature described in relation to any one of the above
aspects may be applied mutatis mutandis to any other aspect.
Furthermore except where mutually exclusive any feature described
herein may be applied to any aspect and/or combined with any other
feature described herein.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments will now be described by way of example only, with
reference to the Figures, in which:
FIG. 1 is a sectional side view of a gas turbine engine;
FIG. 2 is a schematic section of an electrical machine in a first
state;
FIG. 3 shows the machine of FIG. 2 in a second state;
FIG. 4 is a schematic section of an electrical machine in a first
state;
FIG. 5 shows the machine of FIG. 4 in a second state;
FIG. 6 is a schematic section of an electrical machine in a first
state;
FIG. 7 shows the machine of FIG. 6 in a second state;
FIG. 8 a schematic section of another electrical machine in a first
state;
FIG. 9 shows the machine of FIG. 8 in a second state;
FIG. 10 also shows the machine of FIG. 8 in the second state with
another actuator;
FIG. 11 is a schematic section of another electrical machine in a
second state;
FIG. 12 is a schematic section of another electrical machine in a
second state;
FIG. 13 is a schematic section of another electrical machine in a
second state; and
FIG. 14 is a schematic section of another electrical machine in a
second state.
DETAILED DESCRIPTION
With reference to FIG. 1, a gas turbine engine is generally
indicated at 10, having a principal and rotational axis 11. The
engine 10 comprises, in axial flow series, an air intake 12, a
propulsive fan 13, an intermediate pressure compressor 14, a
high-pressure compressor 15, combustion equipment 16, a
high-pressure turbine 17, an intermediate pressure turbine 18, a
low-pressure turbine 19 and an exhaust nozzle 20. A nacelle 21
generally surrounds the engine 10 and defines both the intake 12
and the exhaust nozzle 20.
The gas turbine engine 10 works in the conventional manner so that
air entering the intake 12 is accelerated by the fan 13 to produce
two air flows: a first air flow into the intermediate pressure
compressor 14 and a second air flow which passes through a bypass
duct 22 to provide propulsive thrust. The intermediate pressure
compressor 14 compresses the air flow directed into it before
delivering that air to the high pressure compressor 15 where
further compression takes place.
The compressed air exhausted from the high-pressure compressor 15
is directed into the combustion equipment 16 where it is mixed with
fuel and the mixture combusted. The resultant hot combustion
products then expand through, and thereby drive the high,
intermediate and low-pressure turbines 17, 18, 19 before being
exhausted through the nozzle 20 to provide additional propulsive
thrust. The high 17, intermediate 18 and low 19 pressure turbines
drive respectively the high pressure compressor 15, intermediate
pressure compressor 14 and fan 13, each by suitable interconnecting
shaft.
Other gas turbine engines to which the present disclosure may be
applied may have alternative configurations. By way of example such
engines may have an alternative number of interconnecting shafts
(e.g. two) and/or an alternative number of compressors and/or
turbines. Further the engine may comprise a gearbox provided in the
drive train from a turbine to a compressor and/or fan.
An electrical machine 28 is shown in FIG. 2. Such an electrical
machine 28 may be used as a generator within a gas turbine engine
10 to provide electrical power. For example the electrical machine
28 may provide electrical power to pumps or valves on the engine
10. The electrical machine 28 may also be the main aircraft
generator which provides power to the airframe. Electrical power
generated by the electrical machine 28 may be delivered to an
aircraft powered by the engine 10 for cabin systems such as in-seat
entertainment.
The electrical machine 28 may be mounted to or be integral with an
interconnecting shaft of the engine 10. Thus the electrical machine
28 may be mounted to or be integral with the low pressure shaft,
between the low pressure turbine 19 and fan 13, with the
intermediate pressure shaft, between the intermediate pressure
turbine 18 and intermediate pressure compressor 14, or with the
high pressure shaft, between the high pressure turbine 17 and high
pressure compressor 15.
FIG. 2 shows a shaft 30 of the electrical machine 28 which may be
one of the interconnecting shafts of the gas turbine engine 10. The
electrical machine 28 includes a rotor 32 which is mounted to or
integral with the shaft 30 and which rotates around a rotational
axis 26 which may be coincident with the rotational axis 11. The
rotor 32 is a two-part rotor. A first rotor part 34 is radially
inside a second rotor part 36.
The first rotor part 34 includes a section 38 which is conical. The
conical section 38 may extend the full axial length of the rotor 32
or may be shorter. In the latter case there is one or more
additional section of the first rotor part 34 which is cylindrical
or otherwise not conical. When the electrical machine 28 operates
as a generator the first rotor part 34 is driven mechanically by
the shaft 30. The shaft 30 may be mounted in a non-rotating housing
40 via bearings 42. The first rotor part 34 does not form part of
the electromagnetic circuit of the electrical machine 28.
The second rotor part 36 is positioned radially outside the first
rotor part 34 and has a bore 44. The bore 44 includes a section 46
which is conical and complementary to the conical section 38 of the
first rotor part 34. The second rotor part 36 is supported on the
shaft 30 by further bearings 48 so that it rotates freely on the
shaft 30 and its rotation is driven by the first rotor part 34, as
will be described below. The second rotor part 36 includes an
annular array of permanent magnets 50 on its outer periphery.
Mounted to the housing 40 and positioned radially outside the rotor
32 is a stator 52 of the electrical machine 28. The stator 52
includes electrical coils. In operation of the electrical machine
28 as a generator the rotation of the rotor 32 and the consequent
rotating magnetic field produced by the permanent magnets 50
induces a current in the coils of the stator 52.
To stop a permanent magnet electrical machine from generating, in
response to a fault or otherwise, it is necessary to stop the rotor
from rotating since the magnetism of the permanent magnets cannot
be reversibly switched off. If the electrical machine is driven
from an interconnecting shaft of a gas turbine engine 10 it is not
possible to stop the shaft from rotating without shutting down the
engine.
The disclosed electrical machine 28 overcomes this problem by
virtue of the two-part rotor 32. In normal operation of the
electrical machine 28 as a generator the conical section 46 of the
second rotor part 36 is positioned to abut with the complementary
conical section 38 of the first rotor part 34. The frictional
contact between the conical surfaces engages the two parts 34, 36
of the rotor 32 together and causes them to rotate together as
driven by rotation of the shaft 30.
However, where a fault occurs the electrical machine 28 can be
stopped from generating without having to stop the shaft 30
rotating. To do this the second rotor part 36 is displaced or
translated axially relative to the first rotor part 34. The
displaced position is shown in FIG. 3. By axially displacing the
second rotor part 36 relative to the first rotor part 34 a radial
gap 60 is opened between the complementary conical sections 38, 46
and thus the first and second rotor parts 34, 36 are disengaged.
Thus the second rotor part 36 is no longer driven by the rotation
of the shaft 30 and so slows to a halt. The rate at which it slows
is dependent on the mass of the second rotor part 36, and therefore
its inertia, and the inherent eddy currents which produce a braking
torque.
Since the second rotor part 36 is no longer rotating the magnetic
field generated by the permanent magnets 50 no longer rotates and
so no current is induced in the coils of the stator 52. Therefore
the electrical machine 28 stops generating electricity but the
shaft 30, and the first rotor part 34, continue to rotate.
Advantageously the shaft 30 may therefore be an interconnecting
shaft of the engine 10 because it is not necessary to stop, break
or interrupt the shaft 30 in order to stop the electrical machine
28 generating.
The electrical machine 28 includes a clutch 54. The clutch 54 has
an engaged state and a disengaged state. One of the engaged and
disengaged states of the clutch 54 corresponds to the second rotor
part 36 being engaged with the first rotor part 34 whilst the other
of the engaged and disengaged states of the clutch 54 corresponds
to the second rotor part 36 being axially displaced from, and thus
disengaged from, the first rotor part 34. In FIG. 2 and FIG. 3 the
second rotor part 36 is engaged with the first rotor part 34 when
the clutch 54 is in its disengaged state and vice versa. However,
this relationship may be reversed with equal felicity.
The clutch 54 shown in FIG. 2 and FIG. 3 is an electromagnetic
actuator. The clutch 54 has a non-rotating (stationary) part 56 and
a rotating part 58. The non-rotating part 56 may include a DC coil.
The rotating part 58 may be coupled to or be part of the second
rotor part 36. The rotating part 58 may be a ferromagnetic plate,
for example comprising iron, which may be annular.
In the disengaged, or de-energised, state of the clutch 54 the
rotating and non-rotating parts 58, 56 are axially spaced apart so
that the rotating part 58 can freely rotate relative to the
non-rotating part 56. In the engaged state of the clutch 54, when
it is energised, the rotating part 58 is drawn to the non-rotating
part 56 and electromagnetically locked thereto. The rotating part
58 therefore no longer rotates when it is electromagnetically
locked to the non-rotating part 56.
The clutch 54 acts to axially translate or displace the second
rotor part 36 relative to the first rotor part 34. Consequently the
rotating part 58 of the clutch 54 is mounted to, coupled to or
integrally formed with the second rotor part 36, for example on an
axial end face of the second rotor part 36. The rotating part 58
therefore rotates with the second rotor part 36. When the DC coil
in the non-rotating part 56 of the clutch 54 is energised the
rotating part 58 is drawn axially towards the non-rotating part 56
which consequently draws the second rotor part 36 axially towards
the non-rotating part 56 of the clutch 54. This disengages the
first and second rotor parts 34, 36 and opens the radial gap 60
there between. The second rotor part 36 and rotating part 58 of the
clutch 54 are slowed to a halt by the combination of inertia and
friction between the ferromagnetic plate 58 and the non-rotating
part 56 of the clutch 54. The first rotor part 34 continues to
rotate as driven by rotation of the shaft 30. Since the permanent
magnets 50 no longer rotate no current is induced in the coils in
the stator 52 and so the permanent magnet electrical machine 28 is
safely but reversibly stopped from generating.
The electrical machine 28 may include a bias member 62, illustrated
as a spring, which acts between a stop 64 and an inner bearing race
66. The stop 64 is mounted to or integral with the shaft 30 and
rotates therewith. The inner bearing race 66 is mounted to or
integral with the shaft 30 and is for the bearing 48 at the end of
the second rotor part 36 close to the clutch 54. The inner bearing
race 66 includes a radial lip. When the clutch 54 is engaged, so
that the ferromagnetic plate 58 is drawn towards the non-rotating
part 56, the spring 62 is compressed because the inner bearing race
66 slides on the shaft 30 due to the bearings 48 pushing axially
against the radial lip.
When the clutch 54 is disengaged by virtue of the current to the DC
coil in the non-rotating part 56 being stopped, the compression of
the spring 62 is relaxed and it returns to its relaxed length. As a
consequence, the inner bearing race 66 is pushed axially towards
the first rotor part 34. Due to the radial lip the bearing 48 and
the second rotor part 36 are also moved axially away from the
clutch 54. The spring 62 therefore biases the second rotor part 36
into frictional contact with the first rotor part 34. The bias is
overcome by energising the clutch 54. In the event of a failure or
loss of power to the coil the rotor 32 defaults to its engaged
state because the clutch 54 is not energised.
FIG. 4 is equivalent to FIG. 2 and FIG. 5 is equivalent to FIG. 3
except for the composition of the clutch 54 and its operation. As
well as a DC coil the clutch 54 includes one or more permanent
magnets in its non-rotating part 56. Thus the clutch 54 is a
parallel polarised permanent magnet actuator, or hybrid excited
actuator, which produces an attraction force in the absence of
current in the coil. Thus the clutch 54 as illustrated in FIG. 4
and FIG. 5 acts in the opposite manner to that illustrated in FIG.
2 and FIG. 3 so that the rotor parts 34, 36 of the electrical
machine 28 are disengaged when the clutch 54 is energised and are
engaged when the clutch 54 is de-energised. In the event of a
failure or loss of power to the coil the rotor 32 defaults to its
disengaged state because the clutch 54 is energised.
FIG. 6 and FIG. 7 are similar to FIG. 2 and FIG. 3 respectively.
The rotor parts 34, 36 of the electrical machine 28 are engaged in
FIG. 6 and are disengaged in FIG. 7. However, in FIG. 6 and FIG. 7
the conical sections 38, 46 are inclined in the opposite direction
to those in FIG. 2 and FIG. 3. Thus when the clutch 54 is engaged
the second rotor part 36 is in frictional contact with the first
rotor part 34 and when the clutch 54 is disengaged the second rotor
part 36 is axially spaced from the first rotor part 36, the radial
gap 60 separates the parts 34, 36 and the rotor 32 is
disengaged.
In the arrangement shown in FIG. 6 and FIG. 7 the bias member,
spring 62, acts to bias the second rotor part 36 into its
disengaged state where the radial gap 60 is opened between the
first and second rotor parts 34, 36.
The alternative configuration of the clutch 54 is also applicable
to the oppositely inclined rotor parts 34, 36 shown in FIG. 6 and
FIG. 7. Thus the clutch 54 may have one or more permanent magnets
in its non-rotating part 56 and therefore attract in the absence of
current through the coil.
FIG. 8 and FIG. 9 show a further arrangement of the electrical
machine 28 having the rotor 32 engaged and disengaged respectively.
The first rotor part 34 has two conical sections 38 with a
cylindrical section between them. The second rotor part 36 has two
conical sections 46 to its bore 44 which correspond to the two
conical sections 38 of the first rotor part 34. The section of bore
44 between the conical sections 46 may be cylindrical and is at a
greater radius than the outer surface of the first rotor part 34.
The diameter of the cylindrical section of the bore 44 may be
slightly or greatly wider than the diameter of the first rotor part
34.
Axial translation of the second rotor part 36 due to engagement of
the clutch 54 opens the radial gap 60 between the respective
conical sections 38, 46, as shown in FIG. 9. The conical sections
38, 46 may alternatively be inclined in the opposite direction so
that engaging the clutch 54 engages the complementary conical
sections 38, 46 and so couples the second rotor part 34 to the
first rotor part 36. Providing two, or more, complementary conical
sections 38, 46 may improve the rotor dynamics in some applications
of the electrical machine 28.
FIG. 8 and FIG. 9 also show iron laminations 68 in the second rotor
part 34. The iron laminations are radially inside the permanent
magnets 50.
FIG. 10 is similar to FIG. 9 but includes the alternative version
of the clutch 54 which has one or more permanent magnets in its
non-rotating part 56 and therefore attracts in the absence of
current through the coil.
An alternative configuration of the first and second rotor parts
34, 36 is shown in FIG. 11. Again there are two complementary
conical sections 38, 46 with cylindrical sections between the
conical sections. The two conical sections 38 of the first rotor
part 34 extend radially by the same distance so that all the
cylindrical sections are the same diameter. The conical sections 46
of the bore 44 of the second rotor part 36 are correspondingly the
same radial dimensions as each other the remainder of the bore 44
is cylindrical with a constant diameter. These shapes of first and
second rotor parts 34, 36 can be used with any configuration of the
clutch 54 and with or without iron laminations 68 in the active
second rotor part 36.
The upper half of FIG. 11 shows the conical sections 38, 46 with
the incline in one direction. The lower half of the figure shows
the conical sections inclined in the opposite direction. As will be
apparent to the reader, these are alternatives. In practical
implementations of the electrical machine 28 the inclines would be
in the same direction around the full outer periphery of the first
rotor part 34 and inner periphery of the second rotor part 36.
FIG. 12 is similar to the electrical machine 28 shown in FIG. 8 and
FIG. 9. A pair of axially spaced discs 70 is provided mounted to
the shaft 30 via bearings 72. The shaft 30 may include protrusions
or other features to retain the discs 70 at the required axially
positions. There is an axial space between the housing 40 and the
disc 70, and between the disc 70 and the rotor 32 at each axial
end. The second rotor part 36 includes a rod portion 74 at each end
which extends into or through a bush 76 in each disc 70. The second
rotor part 36, whether engaged with the first rotor part 34 or not,
can therefore rotate independently of the discs 70. The rotating
part 58 of the clutch 54 is mounted to the end of the rod portion
74 so that it is mounted on the opposite axial side of the disc 70
to the rotor 32.
When the clutch 54 includes only a DC coil in its non-rotating part
56 the bias member 62 may comprise a Belleville washer. The
Belleville washer may be mounted on the disc 70 so that it is
axially compressible by the second rotor part 36 when the clutch 54
is engaged. The washer pushes the second rotor part 36 axially,
left as illustrated, in the absence of current in the coil of the
clutch 54 so that the first and second rotor parts 34, 36 couple
together.
The Belleville washer may also be used where the clutch 54 includes
one or more permanent magnets and therefore is energised to connect
(engage) instead of to disconnect (disengage) the rotor parts 34,
36. The spring 62 shown in earlier figures may be replaced by a
Belleville washer. Similarly, the Belleville washer shown in FIG.
12 may be replaced by a spring.
FIG. 13 shows a further configuration of the electrical machine 28
which is similar to FIG. 12. In this configuration the disc 70 is
radially short and includes a compliant member 78. The disc 70 is
shorter than the diameter of the bore 44 of the second rotor part
36. The compliant member 78 extends radially outwardly from the
disc 70 and abuts axially with an end of the second rotor part 36.
There may be one compliant member 78 mounted to each disc 70 so
that there is one compliant member 78 at each axial end of the
rotor 32.
The compliant member 78 at the end which is axially adjacent to the
clutch 54 may be configured to bias the second rotor part 36 into
contact with the first rotor part 34. Hence the bias is towards the
rotor 32. Thus the axial force it exerts must be overcome by the
engagement of the clutch 54 and provides a recovery force to engage
the rotor parts 34, 36 when the clutch 54 is disengaged. Thus the
compliant member 78 acts as the bias member 62 in place of a spring
or Belleville washer.
The compliant member 78 at the other axial end, distal from the
clutch 54, may be biased in the opposite direction. Hence it is
also biased towards the rotor 32. Thus it is biased to push the
second rotor part 36 axially to open the radial gap 60 between the
first and second rotor parts 34, 36. When the clutch 54 is
disengaged the bias of this compliant member 78 is balanced by the
opposite force of the other compliant member 78. Advantageously
this bias accelerates the radial separation of the rotor parts 34,
36 when the clutch 54 is engaged.
The compliant members 78 may be provided by any suitable components
including disk springs, spiral disk springs and Belleville washers.
The compliant members 78 may also be used where the clutch 54
includes one or more permanent magnets and therefore is energised
to connect (engage) instead of to disconnect (disengage) the rotor
parts 34, 36.
A further configuration of the electrical machine 28 is shown in
FIG. 14. The configuration is similar to that shown in FIG. 2 and
FIG. 3 except for the manner in which the second rotor part 36 is
mounted. At the end of the rotor 32 which is distal to the clutch
54 there is a bearing 48. One of the races of the bearing 48 is
mounted to the housing 40 via a static protrusion or otherwise. The
other race is provided on or coupled to the second rotor part 36 so
that the second rotor part 36 is able to rotate relative to the
static housing 40. There is a further bearing 48 at the same end as
the clutch 54. The bearing 48 acts between races, one of which is
provided on or coupled to the second rotor part 36. The other race
is coupled to, formed with or mounted to an extension of the
rotating part 58 of the clutch 54. A Belleville washer 82 or other
bias member may be provided between the rotating part 58, actuator,
of the clutch 54 and the housing 40. The Belleville washer 82
provides a return force when the clutch 54 is de-energised and
thereby assists the axial separation, disengagement, of the second
rotor part 36 from the first rotor part 34.
The alternative configuration of the clutch 54 is also applicable
to the electrical machine 28 as shown in FIG. 14. Thus the clutch
54 may have one or more permanent magnets in its non-rotating part
56 and therefore attract in the absence of current through the
coil.
Mounting the second rotor part 36 from the housing 40, via bearings
48, rather than from the shaft 30 can be applied to any of the
configurations of the electrical machine 28 described herein. Thus
it is applicable whether the conical surfaces 38, 46 are inclined
towards or away from the clutch 54; whether there is one or more
than one pair of complementary conical surfaces 38, 46; whether the
clutch 54 is arranged to engage or disengage to bring the first and
second rotor parts 34, 36 into engagement; and with any form of
bias means to provide a return force on the rotor parts 34, 36
which is opposed to the force generated by the clutch 54 when
energised.
The complementary conical surface 38 of the first rotor part 34 and
conical surface 46 of the second rotor part 36 may engage by
frictional contact. Alternatively they may include positive
engagement features. The positive engagement features may be, for
example, complementary splines or profiled teeth. The splines may
include end sections which guide the splines on the second rotor
part 36 into correct intermeshing relation with the splines on the
first rotor part 34, for example a throat shape on one set of
splines to draw the other set of splines into correct alignment.
Advantageously splines or similar positive engagement features
improve the engagement between the first and second rotor parts 34,
36. However, the provision of splines may require greater axial
translation of the second rotor part 36 in order to disengage the
first and second rotor parts 34, 36.
Advantageously the second rotor part 36 includes inherent eddy
currents which apply a braking torque when it is translated out of
contact with the first rotor part 34. The braking torque therefore
slows the rotation of the second rotor part 36 more quickly to
stationary. The level of eddy currents, and therefore braking
torque, can be enhanced by selecting suitable materials for the
second rotor part 36.
Optionally an anti-rotation feature may be provided on the second
rotor part 36 in order to assist in retarding its rotational speed
when disengaged from the first rotor part 34. For example saliency
or a reluctance feature could be provided to give a small holding
torque. However, such a feature must be designed so that it does
not affect the performance of the electromagnetic actuator, clutch
54.
The angle of incline of the conical surfaces 38, 46 is defined
between the surface and the rotational axis 26 of the electrical
machine 28. Although any angle can be used a range between
8.degree. and 20.degree. inclusive has been found to be practical.
Greater angles, that is a steeper conical surface 38, 46, reduce
the mean diameter of the rotor 32 and therefore reduce the torque
transmission capability. Conversely, shallower angles reduce the
axial force required to translate the second rotor part 36 and
therefore reduce the required size of the electromagnetic actuator,
clutch 54. However, too shallow an angle may lead the rotor parts
34, 36 to bind together meaning they do not release when the axial
force is removed. In some embodiments the tangent to the angle of
incline can be set to be greater than or equal to the coefficient
of friction between the rotor parts 34, 36.
Where there are two or more complementary conical surfaces 38, 46
the angles of incline may be the same. Advantageously the surfaces
engage and disengage at the same point and the same rate.
Alternatively the angle of incline of one of the pairs of
complementary conical surfaces 38, 46 may be different to the angle
of incline of the other pair, or one of the other pairs, of
complementary conical surfaces 38, 46. Advantageously in this way
the engagement surfaces can be fine-tuned for a given torque
transmission requirement. Although two pairs of complementary
conical surfaces 38, 46 could be inclined in the opposite direction
to the rotational axis 26, for example at 8.degree. and -8.degree.
respectively or at -8.degree. and 10.degree. respectively, this
makes assembly of the electrical machine 28 challenging.
Where pairs of complementary conical surfaces 38, 46 are inclined
at different angles the mean radius, maximum radius, and/or minimum
radius may be the same as other pairs, similar to the electrical
machine 28 in FIG. 11, or may be different, similar to FIG. 8.
The electrical machine 28 can also be operated as a motor. In this
case a current is applied to the coils of the stator 52. The
current affects the magnetic flux of the permanent magnets 50
thereby causing the magnetic field to rotate. Consequently the
rotor 32 rotates and so mechanical power is extracted from the
rotation of the shaft 30.
Although the electrical machine 28 has been described in the
context of a gas turbine engine 10 to power an aircraft it is also
applicable where the gas turbine engine 10 is used to power a
marine vessel or land-based power plant. The electrical machine 28
is also suitable for use with a wind turbine or tidal turbine; with
a diesel generator; and as a power pack for a rail vehicle.
It will be understood that the invention is not limited to the
embodiments above-described and various modifications and
improvements can be made without departing from the concepts
described herein. Except where mutually exclusive, any of the
features may be employed separately or in combination with any
other features and the disclosure extends to and includes all
combinations and sub-combinations of one or more features described
herein.
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